1. Field of the Invention
This invention relates to moving imagery projection systems and in particular to systems for projecting images generated by computergraphic technology and formed by an intense light beam or beams on a geometric, e.g., curvilinear, domed, or spherical, viewing surface. The invention is particularly suitable for use in planetariums to augment existing starfields and other conventional incandescent projection devices.
2. Description of the Related Art
The combination of state-of-the-art computergraphic technology with various images of projection equipment has produced a variety of projection systems for generating images on a viewing surface. The computergraphic technology has allowed operators to create, retrieve, and manipulate graphic images on laptop or desktop computers. See U.S. Pat. No. 4,763,280 to Robinson et al.; U.S. Pat. No. 4,347,507 to Spooner. Using a variety of light sources, these images have been projected on viewing surfaces having a variety of geometric shapes for a varies of purposes. Nevertheless, these systems suffer from significant limitations. For example, as the angle of deflection of the image-generating light beam increases, the images tend to lose resolution, e,g., to become increasingly fuzzy, especially at the edges of the viewing surface. Consequently, the intensity of the images also decreases. Further, in order to project images on a curvilinear viewing surface, it is necessary to greatly increase the angle of deflection of the projected images. This too has caused degradation of the quality of the images.
Perhaps, the two most common uses for these related art systems are as entertainment displays and simulation devices. See U.S. Pat. No. 4,347,507 to Spooner; U.S. Pat. No. 4,100,571 to Dykes et al. In both uses, however, the same problems arise--namely, how to maintain image resolution and intensity and still project onto a curvilinear viewing surface without unacceptable distortion. Conventional viewing surfaces have comprised mosaics of substantially flat viewing surfaces. Such viewing surfaces often require the use of separate projection channels for each flat viewing surface. Even when a curvilinear viewing surface is used, mosaic projection techniques are sometimes employed. See U.S. Pat. No. 4,297,723 to Whitby. Such projection systems, however, can not take full advantage of the seamlessness of the curvilinear viewing surface and its other inherent advantages, such as the lack of discontinuities in the image as the projection system slews the image across the viewing surface. Other problems with a mosaic presentation arise from imperfect seam matching, contrast or color matching, and brightness matching. Imperfections in any of these areas are readily noticed by viewers, and because even slight matching imperfections are generally noticeable on large projections, it is very difficult to eliminate these problems. Further, the seamless presentation possible from a curvilinear viewing surface is easier to watch, e.g., causes less eye strain, and creates a more realistic presentation, and continuous curvilinear viewing surfaces may also be easier to manufacture.
Related art projection systems have not been able to successfully project sufficiently distinct and intense graphic images on a domed or spherical viewing surface. Some systems, such as that disclosed in U.S. Pat. No. 4,763,280 to Robinson et al., appear to disclose a system for achieving at least 180 degrees by 180 degrees or hemispherical projections. Others, such as that disclosed in U.S. Pat. No. 4,100,571 to Dykes et al., appear to disclose a system for achieving at least 360 degrees by 90 degrees. Neither of these systems, however, seems capable of projecting a sufficiently distinct and moving image on a spherical viewing surface without employing multiple projection channels.
As mentioned above, systems for projecting moving imagery on curvilinear viewing surfaces have found many military and training applications, especially in the field of flight simulation. In these applications, a realistic ambient environmental simulation or model board image may be projected onto a viewing surface, so that a pilot or other trainee may react to it and so that the image can be altered in response to the actions and reactions of the pilot or trainee. These images are commonly generated by means of a high-resolution cathode ray tube (CRT) or a high-resolution closed circuit television (CCT) projector. See U.S. Pat. No. 4,297,723 to Whitby; U.S. Pat. No. 4,100,571 to Dykes et al. Images generated in this manner, however, may also present significant disadvantages. First, such generating devices may be more suitable for mosaic presentations and suffer from the same mosaic limitations discussed above. Second, when a CRT or CCT projection is deflected or projected through a wide angle lens, an unacceptable amount of distortion may occur. The resulting image is fuzzy, blurred, or indistinct, which detracts from the training or simulation benefits of the system. Unlike these systems, images projected by the present invention may be similar to computergraphic images, rather than to the photo-realistic images generated by a system using CRT or CCT technology.
Various attempts have been made to develop projection systems which improve the projected images resolution and intensity. By using a laser beam, the intensity of which is modulated with video information by means of an acousto-optic cell, images have been scanned in a raster pattern onto a viewing surface. These systems may provide improved brightness due to the greater intensity inherent in a laser. See U.S. Pat. No. 3,992,718 to Driskell. Nevertheless, simply expanding the scanning window does not eliminate resolution problems, and the desired resolution can not be attained from his system without undesirable modifications. In order to avoid the resolution problems in a simulator, a CRT system must operate at a high bandwidth. The amount of bandwidth necessary increases, as the desired level of resolution increases. For example, television requires a bandwidth in the order of about 10 MHz to adequately transmit the signals necessary to generate the individual points in a 625 line television picture and to repeat the picture signals twenty-five (25) times per second. In order to generate a field of view of even 175 degrees by 75 degrees, therefore, might require a bandwidth of approximately 100 MHz to achieve the resolution demanded in modern flight simulation. This, however, places additional demands on the modulation of the laser beam and may make the system incompatible with digital image generating systems used in simulators.
The present invention allows a moving image to be projected with sufficient size, intensity, and clarity to fill an entire domed or spherical viewing surface, i.e., about 360 degrees by at least 180 degrees, and to avoid the loss of resolution and intensity experienced with other projection systems. Moreover, when the beam is static, instead of dynamic, an intense point of light is projected on the domed or spherical viewing surface.